As of Notepad++ 5.9 they added a feature to 'Remove Unmarked Lines' which can be used to strip away everything that you don't want along with some search and replaces for the other text on each value line.
You can also do a similar thing using Search-->Bookmark-->Copy Bookmarked Lines
So technically you still cannot copy marked text, but you can bookmark lines with marked text and then perform various operations on bookmarked or unmarked lines.